Offer Either::left_opt() and Either::right_opt() and add some test cases

either.h

@@ -2,7 +2,7 @@
 #ifndef MESSMER_CPP_UTILS_EITHER_H
 #define MESSMER_CPP_UTILS_EITHER_H
 
-#include <type_traits>
+#include <boost/optional.hpp>
 
 namespace cpputils {
 
@@ -65,21 +65,50 @@ namespace cpputils {
             return _side == Side::right;
         }
 
-        //TODO Also offer a safe version of getting left/right (exceptions? nullptr?)
         const Left &left() const {
             return _left;
         }
+        Left &left() {
+            return const_cast<Left&>(const_cast<const Either<Left, Right>*>(this)->left());
+        }
 
         const Right &right() const {
             return _right;
         }
-
-        Left &left() {
-            return const_cast<Left&>(const_cast<const Either<Left, Right>*>(this)->left());
-        }
         Right &right() {
             return const_cast<Right&>(const_cast<const Either<Left, Right>*>(this)->right());
         }
+
+        boost::optional<const Left&> left_opt() const {
+            if (_side == Side::left) {
+                return _left;
+            } else {
+                return boost::none;
+            }
+        }
+        boost::optional<Left&> left_opt() {
+            if (_side == Side::left) {
+                return _left;
+            } else {
+                return boost::none;
+            }
+        }
+
+        boost::optional<const Right&> right_opt() const {
+            if (_side == Side::right) {
+                return _right;
+            } else {
+                return boost::none;
+            }
+        }
+        boost::optional<Right&> right_opt() {
+            if (_side == Side::right) {
+                return _right;
+            } else {
+                return boost::none;
+            }
+        }
+
     private:
         union {
             Left _left;

test/EitherTest.cpp

@@ -1,8 +1,16 @@
 #include <google/gtest/gtest.h>
 #include <google/gmock/gmock.h>
+#include <boost/optional/optional_io.hpp>
 #include "../either.h"
 #include "../macros.h"
 
+//TODO Go through all test cases and think about whether it makes sense to add the same test case but with primitive types.
+
+using std::string;
+using std::vector;
+using namespace cpputils;
+using ::testing::Test;
+
 class OnlyMoveable {
 public:
   OnlyMoveable(int value_): value(value_)  {}
@@ -12,9 +20,11 @@ private:
   DISALLOW_COPY_AND_ASSIGN(OnlyMoveable);
 };
 
-using std::string;
-using namespace cpputils;
-using ::testing::Test;
+template<typename T>
+struct StoreWith1ByteFlag {
+  T val;
+  char flag;
+};
 
 class EitherTest: public Test {
 public:
@@ -32,18 +42,39 @@ public:
   void EXPECT_LEFT_IS(const Expected &expected, Either<Left, Right> &value) {
     EXPECT_IS_LEFT(value);
     EXPECT_EQ(expected, value.left());
+    EXPECT_EQ(expected, value.left_opt().get());
+    EXPECT_EQ(boost::none, value.right_opt());
     const Either<Left, Right> &const_value = value;
     EXPECT_EQ(expected, const_value.left());
+    EXPECT_EQ(expected, const_value.left_opt().get());
+    EXPECT_EQ(boost::none, const_value.right_opt());
   }
   template<class Left, class Right, class Expected>
   void EXPECT_RIGHT_IS(const Expected &expected, Either<Left, Right> &value) {
     EXPECT_IS_RIGHT(value);
     EXPECT_EQ(expected, value.right());
+    EXPECT_EQ(expected, value.right_opt().get());
+    EXPECT_EQ(boost::none, value.left_opt());
     const Either<Left, Right> &const_value = value;
     EXPECT_EQ(expected, const_value.right());
+    EXPECT_EQ(expected, const_value.right_opt().get());
+    EXPECT_EQ(boost::none, const_value.left_opt());
   }
 };
 
+template<typename Left, typename Right>
+void TestSpaceUsage() {
+  EXPECT_EQ(std::max(sizeof(StoreWith1ByteFlag<Left>), sizeof(StoreWith1ByteFlag<Right>)), sizeof(Either<Left, Right>));
+}
+
+TEST_F(EitherTest, SpaceUsage) {
+  TestSpaceUsage<char, int>();
+  TestSpaceUsage<int, short>();
+  TestSpaceUsage<char, short>();
+  TestSpaceUsage<int, string>();
+  TestSpaceUsage<string, vector<string>>();
+}
+
 TEST_F(EitherTest, LeftCanBeConstructed) {
   Either<int, string> val = 3;
   UNUSED(val);
@@ -142,6 +173,30 @@ TEST_F(EitherTest, RightCanBeMoved) {
   EXPECT_EQ(5, val2.right().value);
 }
 
+TEST_F(EitherTest, ModifyLeft) {
+  Either<string, int> val = string("mystring1");
+  val.left() = "mystring2";
+  EXPECT_LEFT_IS("mystring2", val);
+}
+
+TEST_F(EitherTest, ModifyRight) {
+  Either<int, string> val = string("mystring1");
+  val.right() = "mystring2";
+  EXPECT_RIGHT_IS("mystring2", val);
+}
+
+TEST_F(EitherTest, ModifyLeftOpt) {
+  Either<string, int> val = string("mystring1");
+  val.left_opt().get() = "mystring2";
+  EXPECT_LEFT_IS("mystring2", val);
+}
+
+TEST_F(EitherTest, ModifyRightOpt) {
+  Either<int, string> val = string("mystring1");
+  val.right_opt().get() = "mystring2";
+  EXPECT_RIGHT_IS("mystring2", val);
+}
+
 TEST_F(EitherTest, LeftEquals) {
   Either<string, int> val1 = string("mystring");
   Either<string, int> val2 = string("mystring");